Kot Marta, Daniel Władysława A
Department of Pharmacokinetics and Drug Metabolism, Institute of Pharmacology, Polish Academy of Sciences, Smetna 12, PL 31-343 Kraków, Poland.
Biochem Pharmacol. 2008 Apr 1;75(7):1538-49. doi: 10.1016/j.bcp.2007.12.017. Epub 2008 Jan 5.
The aim of the present study was to estimate the relative contribution of rat P450 isoforms to the metabolism of caffeine and to assess the usefulness of caffeine as a marker substance for estimating the activity of P450 in rat liver and its potential for pharmacokinetic interactions in pharmacological experiments. The results obtained using rat cDNA-expressed P450s indicated that 8-hydroxylation was the main oxidation pathway of caffeine (70%) in the rat. CYP1A2 was found to be a key enzyme catalyzing 8-hydroxylation (72%) and substantially contributing to 3-N-demethylation (47%) and 1-N-demethylation (37.5%) at a caffeine concentration of 0.1mM (relevant to "the maximum therapeutic concentration in humans"). Furthermore, CYP2C11 considerably contributed to 3-N-demethylation (31%). The CYP2C subfamily (66%) - mainly CYP2C6 (27%) and CYP2C11 (29%) - played a major role in catalyzing 7-N-demethylation. At higher substrate concentrations, the contribution of CYP1A2 to the metabolism of caffeine decreased in favor of CYP2C11 (N-demethylations) and CYP3A2 (mainly 8-hydroxylation). The obtained results were confirmed with liver microsomes (inhibition and correlation studies). Therefore, caffeine may be used as a marker substance for assessing the activity of CYP1A2 in rats, using 8-hydroxylation (but not 3-N-demethylation-like in humans); moreover, caffeine may also be used to simultaneously, preliminarily estimate the activity of CYP2C using 7-N-demethylation as a marker reaction. Hence caffeine pharmacokinetics in rats may be changed by drugs affecting the activity of CYP1A2 and/or CYP2C, e.g. by some antidepressants.
本研究的目的是评估大鼠P450同工酶对咖啡因代谢的相对贡献，并评估咖啡因作为一种标记物质在估计大鼠肝脏中P450活性以及在药理实验中其药代动力学相互作用潜力方面的实用性。使用大鼠cDNA表达的P450所获得的结果表明，8-羟基化是大鼠体内咖啡因的主要氧化途径（70%）。在咖啡因浓度为0.1mM（与“人类最大治疗浓度”相关）时，发现CYP1A2是催化8-羟基化的关键酶（72%），并且对3-N-去甲基化（47%）和1-N-去甲基化（37.5%）有显著贡献。此外，CYP2C11对3-N-去甲基化有相当大的贡献（31%）。CYP2C亚家族（66%）——主要是CYP2C6（27%）和CYP2C11（29%）——在催化7-N-去甲基化中起主要作用。在较高底物浓度下，CYP1A2对咖啡因代谢的贡献降低，有利于CYP2C11（N-去甲基化）和CYP3A2（主要是8-羟基化）。所获得的结果通过肝微粒体（抑制和相关性研究）得到证实。因此，咖啡因可以用作评估大鼠体内CYP1A2活性的标记物质，采用8-羟基化（而不是像人类那样的3-N-去甲基化）；此外，咖啡因还可以用作同时初步估计CYP2C活性的标记反应，以7-N-去甲基化作为标记反应。因此，影响CYP1A2和/或CYP2C活性的药物，例如某些抗抑郁药，可能会改变大鼠体内咖啡因的药代动力学。
